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author | Amar Takhar <amar@rtems.org> | 2016-01-17 00:47:50 -0500 |
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committer | Amar Takhar <verm@darkbeer.org> | 2016-05-02 20:51:23 -0400 |
commit | b35050917272ab536c8f4158e5c002f98a092796 (patch) | |
tree | 386dc0be827a10ff668e6d0b2b1ff52a1f49e9ed /bsp_howto/target_dependant_files.rst | |
parent | Fix warnings. (diff) | |
download | rtems-docs-b35050917272ab536c8f4158e5c002f98a092796.tar.bz2 |
Split document into seperate files by section.
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diff --git a/bsp_howto/target_dependant_files.rst b/bsp_howto/target_dependant_files.rst new file mode 100644 index 0000000..77a78f1 --- /dev/null +++ b/bsp_howto/target_dependant_files.rst @@ -0,0 +1,232 @@ +Target Dependent Files +###################### + +RTEMS has a multi-layered approach to portability. This is done to +maximize the amount of software that can be reused. Much of the +RTEMS source code can be reused on all RTEMS platforms. Other parts +of the executive are specific to hardware in some sense. +RTEMS classifies target dependent code based upon its dependencies +into one of the following categories. + +- CPU dependent + +- Board dependent + +- Peripheral dependent + +CPU Dependent +============= + +This class of code includes the foundation +routines for the executive proper such as the context switch and +the interrupt subroutine implementations. Sources for the supported +processor families can be found in ``cpukit/score/cpu``. +A good starting point for a new family of processors is the``no_cpu`` directory, which holds both prototypes and +descriptions of each needed CPU dependent function. + +CPU dependent code is further subcategorized if the implementation is +dependent on a particular CPU model. For example, the MC68000 and MC68020 +processors are both members of the m68k CPU family but there are significant +differences between these CPU models which RTEMS must take into account. + +The source code found in the ``cpukit/score/cpu`` is required to +only depend upon the CPU model variations that GCC distinguishes +for the purposes of multilib’ing. Multilib is the term the GNU +community uses to refer to building a single library source multiple +times with different compiler options so the binary code generated +is compatible. As an example, from GCC’s perspective, many PowerPC +CPU models are just a PPC603e. Remember that GCC only cares about +the CPU code itself and need not be aware of any peripherals. In +the embedded community, we are exposed to thousands of CPU models +which are all based upon only a relative small number of CPU cores. + +Similarly for the SPARC/ERC32 BSP, the ``RTEMS_CPU`` is specified as``erc32`` which is the name of the CPU model and BSP for this SPARC V7 +system on chip. But the multilib variant used is actually ``v7`` +which indicates the ERC32 CPU core is a SPARC V7. + +Board Dependent +=============== + +This class of code provides the most specific glue between RTEMS and +a particular board. This code is represented by the Board Support Packages +and associated Device Drivers. Sources for the BSPs included in the +RTEMS distribution are located in the directory ``c/src/lib/libbsp``. +The BSP source directory is further subdivided based on the CPU family +and BSP. + +Some BSPs may support multiple board models within a single board family. +This is necessary when the board supports multiple variants on a +single base board. For example, the Motorola MVME162 board family has a +fairly large number of variations based upon the particular CPU model +and the peripherals actually placed on the board. + +Peripheral Dependent +==================== + +This class of code provides a reusable library of peripheral device +drivers which can be tailored easily to a particular board. The +libchip library is a collection of reusable software objects that +correspond to standard controllers. Just as the hardware engineer +chooses a standard controller when designing a board, the goal of +this library is to let the software engineer do the same thing. + +The source code for the reusable peripheral driver library may be found +in the directory ``c/src/lib/libchip``. The source code is further +divided based upon the class of hardware. Example classes include serial +communications controllers, real-time clocks, non-volatile memory, and +network controllers. + +Questions to Ask +================ + +When evaluating what is required to support RTEMS applications on +a particular target board, the following questions should be asked: + +- Does a BSP for this board exist? + +- Does a BSP for a similar board exists? + +- Is the board’s CPU supported? + +If there is already a BSP for the board, then things may already be ready +to start developing application software. All that remains is to verify +that the existing BSP provides device drivers for all the peripherals +on the board that the application will be using. For example, the application +in question may require that the board’s Ethernet controller be used and +the existing BSP may not support this. + +If the BSP does not exist and the board’s CPU model is supported, then +examine the reusable chip library and existing BSPs for a close match. +Other BSPs and libchip provide starting points for the development +of a new BSP. It is often possible to copy existing components in +the reusable chip library or device drivers from BSPs from different +CPU families as the starting point for a new device driver. +This will help reduce the development effort required. + +If the board’s CPU family is supported but the particular CPU model on +that board is not, then the RTEMS port to that CPU family will have to +be augmented. After this is done, development of the new BSP can proceed. + +Otherwise both CPU dependent code and the BSP will have to be written. + +This type of development often requires specialized skills. If +you need help in making these modifications to RTEMS, please +consider using one of the RTEMS Service Providers. The current +list of these is at http://www.rtems.org/support.html. + +CPU Dependent Executive Files +============================= + +The CPU dependent files in the RTEMS executive source code are found +in the following directory: +.. code:: c + + cpukit/score/cpu/*CPU* + +where *CPU* is replaced with the CPU family name. + +Within each CPU dependent directory inside the executive proper is a +file named ``*CPU*.h`` which contains information about each of the +supported CPU models within that family. + +CPU Dependent Support Files +=========================== + +The CPU dependent support files contain routines which aid in the development +of applications using that CPU family. For example, the support routines +may contain standard trap handlers for alignment or floating point exceptions +or device drivers for peripheral controllers found on the CPU itself. +This class of code may be found in the following directory: + +.. code:: c + + c/src/lib/libcpu/*CPU* + +CPU model dependent support code is found in the following directory: + +.. code:: c + + c/src/lib/libcpu/*CPU*/*CPU_MODEL* + +*CPU_MODEL* may be a specific CPU model name or a name indicating a CPU +core or a set of related CPU models. The file ``configure.ac`` in each ``c/src/lib/libcpu/*CPU*`` directory contains the logic which enables +the appropriate subdirectories for the specific CPU model your BSP has. + +Board Support Package Structure +=============================== + +The BSPs are all under the ``c/src/lib/libbsp`` directory. Below this +directory, there is a subdirectory for each CPU family. Each BSP +is found under the subdirectory for the appropriate processor +family (m68k, powerpc, etc.). In addition, there is source code +available which may be shared across all BSPs regardless of +the CPU family or just across BSPs within a single CPU family. This +results in a BSP using the following directories: +.. code:: c + + c/src/lib/libbsp/shared + c/src/lib/libbsp/*CPU*/shared + c/src/lib/libbsp/*CPU*/*BSP* + +Under each BSP specific directory, there is a collection of +subdirectories. For commonly provided functionality, the BSPs +follow a convention on subdirectory naming. The following list +describes the commonly found subdirectories under each BSP. + +- *console*: + is technically the serial driver for the BSP rather + than just a console driver, it deals with the board + UARTs (i.e. serial devices). + +- *clock*: + support for the clock tick – a regular time basis to the kernel. + +- *timer*: + support of timer devices. + +- *rtc* or ``tod``: + support for the hardware real-time clock. + +- *nvmem*: + support for non-volatile memory such as EEPROM or Flash. + +- *network*: + the Ethernet driver. + +- *shmsupp*: + support of shared memory driver MPCI layer in a multiprocessor system, + +- *include*: + include files for this BSP. + +- *gnatsupp*: + BSP specific support for the GNU Ada run-time. Each BSP that wishes + to have the possibility to map faults or exceptions into Ada language + exceptions or hardware interrupts into Ada interrupt tasks must provide + this support. + +There may be other directories in the BSP tree and the name should +be indicative of the functionality of the code within that directory. + +The build order of the BSP is determined by the Makefile structure. +This structure is discussed in more detail in the `Makefiles`_ +chapter. + +*NOTE:* This manual refers to the gen68340 BSP for numerous concrete +examples. You should have a copy of the gen68340 BSP available while +reading this piece of documentation. This BSP is located in the +following directory: +.. code:: c + + c/src/lib/libbsp/m68k/gen68340 + +Later in this document, the $BSP340_ROOT label will be used +to refer to this directory. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + + |